"The Chinese government has followed common international practices in the establishment of the zone, with aims of protecting its state sovereignty and territorial and airspace security, and maintaining flying orders," the government said in a statement accompanying the map. "It is a necessary measure in China's exercise of self-defense rights. It has no particular target and will not affect the freedom of flight in relevant airspace."

USA Today reports that Japan called the unilateral move an escalation of the situation regarding the islands. The paper reports:

"Situated in potentially energy-rich waters, the islands are known as the Senkaku in Japan, and the Diaoyu in China. They remain controlled by Tokyo, but Beijing says they belong to China, and in the past year has grown more assertive in staking that claim, with increased numbers of Chinese boats and planes crossing into Japanese waters and airspace to visit the area.

"Saturday morning, the Chinese air force promptly conducted its first patrol of the new air zone. ...

"The United States is 'deeply concerned' by China's new zone, Secretary of State John Kerry said in a statement Saturday.

"'We view this development as a destabilizing attempt to alter the status quo in the region. This unilateral action increases the risk of misunderstanding and miscalculations,' Kerry said from Geneva, where he was participating in Iran nuclear talks."

The BBC reports that the move is in line with the more muscular posture taken by President Xi Jinping.

"His nationalist approach, backed-up by large increases in spending on the armed forces, is welcomed by many in China. But it has led to increasing tension with almost all of China's neighbours. Many, like Japan, have defence agreements with the United States, which has long sought to preserve the balance of power in Asia.

"The fear is that one small incident, for example between Chinese and Japanese vessels or aircraft, could escalate rapidly into a far wider and more serious crisis."

Bloomberg reports that China said it will take "defensive emergency measures" if an aircraft violates the new boundaries, but the country has not made clear what those measures would be.

China did outline a new set rules it expects aircraft coming into the space to follow.

"The rules include reporting flight plans to China's Foreign Ministry or civil aviation authorities and providing radio and logo identification of aircraft, according to the Defense Ministry," Bloomberg reports.